Habitat

Big-eared opossums live in Atlantic rainforests, secondary Atlantic forests, and Araucaria highlands. They are also found in forests fragmented by urban development and deforestation. Their habitat has are two discrete seasons, a warm rainy season, which lasts from September to March and a cool dry season, which lasts from April to August. The mean annual temperature in their habitat is between 17 and 24°C, with a mean annual rainfall of 1,350 to 2,000 mm. (Caceres and Monteiro-Filho, 2001; Caceres, 2003; Cerqueira and Lemos, 2000; Emmons, 1997; Grelle, 2003; Leite, et al., 1996)

Physical Description

Big-eared opossums closely resemble another Neotropical marsupial, common opossums (Didelphis marsupialis). In fact, this species was once considered a subspecies of D. marsupialis. Big-eared opossums have prominent facial markings and a conspicuous black line down the center of their forehead. Their ears are naked and black. Their fur is dirty yellow, with black or gray tips. Big-eared opossums have long, prehensile tails that are furred at the base. The fur at the base of their tail is about as long as their hind legs and is at least half black and half white; the black portion is sometimes longer. In contrast, common opossums (Didelphis marsupialis) do not have as much fur on the base of their tail and they usually have a shorter black portion. Aside from geographic location, this is one characteristic that can be used to distinguish the species. (Caceres, 2003; Emmons, 1997; Hume, 1999)

Male big-eared opossums tend to be larger than females. Adult males range from 1,500 to 1,880 grams during the reproductive season. Females can weigh anywhere from 1,000 to 1,300 grams in the reproductive season. (Caceres, 2003)

Reproduction

Big-eared opossums are considered promiscuous. The home ranges of non-territorial males overlap with the home ranges of several territorial females and other non-territorial males. Therefore, females defend areas with sufficient resources and males seeking mates roam to find them. Licking and scratching of the cervical scent gland and vocalization helps males find females. (Caceres, 2003; Nogueira and Castro, 2003)

In the case of big-eared opossums, the breeding season coincides with the wet season, when fruit is most abundant. Like other marsupials, big-eared opossums undergo a brief gestation period and give birth to tiny young that crawl into the mother’s pouch where they attach to a nipple and feed for about 100 days. Weaning generally occurs at the end of the rainy season, while food is still available for the young. Females may synchronize their reproduction by photoperiod. Individuals born at the end of the current breeding season are able to reproduce at the start of the next breeding season. Using information from other South American Didelphids like common opossums, females can have 2 to 3 litters per breeding season, with an average of 7.3 young per litter. (Eisenberg and Redford, 1999; Gentile, et al., 2000; Gentile, et al., 1995)

Female big-eared opossums carry young in their pouches until weaning, which could be up to 100 days from birth. This provides protection and nutrition for the under-developed young. (Gentile, et al., 1995)

Parental Investment

pre-weaning/fledging

provisioning

female

protecting

female

Lifespan/Longevity

Little information is available on the lifespan of big-eared opossums, but their close relative common opossums have an average lifespan of 2 years in the wild. (Hagmann, 2003)

Behavior

Big-eared opossums are scansorial, nocturnal and solitary. They are mainly terrestrial, but their relatively long forelimbs and claws allow them to easily climb trees. It has been argued that big-eared opossums are exclusively terrestrial and only go into trees to escape flooding, but other studies have shown that using proper techniques, big-eared opossums can be trapped or tracked in trees as frequently as on the ground. This scansorial behavior may allow for some resource partitioning and alleviate some competition between big-eared opossums and other opossums in the area, like the terrestrial brown four-eyed opossums and the arboreal bare-tailed woolly opossums. (Caceres, 2003; Cerqueira and Lemos, 2000; Cuhna and Vieira, 2002; Leite, et al., 1996)

Home Range

The average home range size for female big-eared opossums is 0.6 to 1.7 hectares in the non-reproductive season and 0.6 to 1.3 hectares in the reproductive season, when resources are more abundant. Females may also have a hierarchy, determining which female get the best territory. Males have a much larger home range of 2.3 to 2.7 hectares. (Caceres, 2003)

Communication and Perception

Big-eared opossums have a cervical scent gland. A scent-marking behavior can release the secretions of this sebaceous gland into the environment, where it is used for social communication. (Nogueira and Castro, 2003)

Ecosystem Roles

Big-eared opossums and other South American marsupials are the preferred host of the tick species Ixodes loricatus. Big-eared opossums prey upon many different kinds of insects and fruits. The latter may help seed dispersal. (Barros-Battesti, et al., 2000)

Conservation Status

Big-eared opossums are one of the most common marsupials in their home range. They were trapped with the highest frequency in most studies conducted in coastal Brazil involving small mammals. However, deforestation rates in that area are high and only 5% of the original rainforest remains. This may pose a threat to big-eared opossums and other rainforest species in the future. (Cuhna and Vieira, 2002; Gentile, et al., 2000; Grelle, 2003; Leite, et al., 1996; Pires, et al., 2002)

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

omnivore

an animal that mainly eats all kinds of things, including plants and animals

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

Gentile, R., P. D'Andrea, R. Cerqueira. 1995. Age structure of two marsupial species in a Brazilian restinga. Journal of Tropical Ecology, 11: 679-682.

Gentile, R., P. D'Andrea, R. Cerqueira, L. Maroja. 2000. Population dynamics and reproduction of marsupials and rodents in a Brazilian rural area: a five year study. Studies on Neotropical Fauna and Environment, 35: 1-9.

Greene, H. 1997. Snakes: The evolution of mystery in nature. Berkeley and Los Angeles, CA: University of California Press.

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Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.